The idea that matching personality expression with situational demands is adaptive is implicit in many accounts of personality. Numerous constructs and measures have been posited to address this or similar phenomena. Few have proven adequate. In response, we proposed and tested a novel measurement approach (the APR index) assessing real-time behavior to rate participants’ success in matching personality expression with situational demands, which we denote adaptive personality regulation. An experimental study (N = 88) and an observational study of comedians (N = 203) provided tests of whether the APR index constituted a useful metric of adaptive personality regulation. In both studies, the APR index showed robust psychometric properties; was statistically unique from mean-level personality, self-monitoring, and the general factor of personality expression; and provided incremental concurrent prediction of task/job performance. The results suggest that the APR index provides a useful metric for studying the phenomenon of successfully matching personality expression to situational demands.